This is a revised application to study the potential of amelogenin pre-mRNA splice products to participate in epithelial-mesenchymal signaling during tooth morphoigenesis. Specific amelogenin mRNA splice products have been shown to have BMP-like activities leading to cartilage/bone induction when implanted into ectopic sites in vivo, and to induce expression of cartilage/bone phenotypic molecules in mesenchymal cells in culture. We have shown that two specific splice products, 73 and 59 amino acids in length, respectively, act by regulating the expression of transcription factors. They have different inductive effects on the development of tooth germs in culture. They also yield different effects on the repair of dentin defects and pulp mineralization. Although the amelogenin genes have been thought to be expressed only in the dental epithelium, amelogenin gene products have been shown to be present in the mantle dentin and we have evidence from in situ hybridization that they may be produced directly in early pre-odontoblasts. Others have shown that amelogenins may be involved in induction of tooth cementum. On the basis of these data we have hypothesized that the amelogenin gene small splice product peptides are transcriptional regulating factors that have a role in the epithelial-mesenchymal signaling that is such a prominent part of tooth development. Three specific aims are proposed for this study: 1) To use in situ hybridization to confirm the presence of amelogenin mRNAs in odontoblasts, and immunohistochemistry to determine the tooth developmental stages at which odontoblasts express the amelogenin gene message, and show the appearance of the peptide products in the odontoblasts; 2)To clarify in detail, using gene arrays and other techniques the effects of the peptides on directing the expression of odontoblast and cementoblast phenotypes during tooth development, in culture; and 3) To more completely determine the mechanisms by which the peptides interact with mesenchymal cells in general to alter their phenotypic expression. Logical extensions of these studies would be to examine, under Aim 2, the use of the peptides in more general heterotypic epithelial-mesenchymal recombination experiments, and, under Aim 3) to analyze the combined effects of the two peptides on the BMP-like activity on the phenotypic expression in mesenchymal cells in bone induction and tooth development. In this revision, more experimental details have been provided.